Mr. Hurd stepped down Friday after a sexual harassment inquiry found that he had filed inaccurate expense reports.

In an impassioned e-mail sent to The New York Times, Mr. Ellison chided H.P.’s board for what he said was a grave mistake.

“The H.P. board just made the worst personnel decision since the idiots on the Apple board fired Steve Jobs many years ago,” Mr. Ellison wrote. “That decision nearly destroyed Apple and would have if Steve hadn’t come back and saved them.”

Oracle, the world’s largest database software maker, has been a close partner of H.P., which sells large computing systems to corporations.

Since its acquisition of Sun Microsystems, completed early this year, Oracle has become a major rival to H.P. in the computing hardware market.

Mr. Ellison and Mr. Hurd, meanwhile, have been close personal friends. Both are avid tennis players, and Mr. Hurd often plays at Mr. Ellison’s house in Silicon Valley.

Mr. Ellison’s attack on the H.P. board focused on questions of corporate governance.

“In losing Mark Hurd, the H.P. board failed to act in the best interest of H.P.’s employees, shareholders, customers and partners,” Mr. Ellison wrote. “The H.P. board admits that it fully investigated the sexual harassment claims against Mark and found them to be utterly false.”

Earlier this year, Oracle’s president, Charles Phillips, admitted to an eight-year relationship with a woman other than his wife. Mr. Phillips continues in the job.

A prominent executive in Silicon Valley, Mr. Ellison has long dealt with executives at H.P. and some of its directors, although he is not on the board. By his account, a debate erupted among H.P. directors over whether the company needed to disclose the sexual harassment claim.

According to Mr. Ellison, the board was split 6 to 4 in preliminary discussions over the disclosure issue, and later decided to make the decision unanimous. He declined to comment on the source of his information.

An H.P. spokesman declined on Monday to address whether a vote on disclosure had taken place, saying only that the vote seeking Mr. Hurd’s resignation was unanimous.

A person with direct knowledge of negotiations between Mr. Hurd and the board of H.P. has said that the disclosure issue stood as the main point of contention in the period leading up to Mr. Hurd’s ouster last week.

Once the board decided to go ahead with the disclosure, this person said, the relationship with Mr. Hurd turned more antagonistic and the parties agreed on the resignation as the way to move forward.

APCO, a public relations firm advising H.P.’s board, told directors that H.P. would face a public relations firestorm if the accusations of sexual harassment were made public, this person said. People close to Mr. Hurd said that he had failed to understand why the board needed to disclose the investigation after the inquiry found the claim baseless.

The H.P. investigation failed to turn up evidence of sexual misconduct by Mr. Hurd, and both he and Jodie Fisher, a 50-year-old actress whom H.P. had hired to work at marketing events, have denied having a romantic relationship.

Ms. Fisher has since settled the matter with Mr. Hurd for an undisclosed sum.

H.P. has said that Mr. Hurd’s resignation was the result of a break in trust caused by his falsifying expense reports to conceal the relationship.